This invention relates to an optical lens which is held by a lens holder, particularly, relates to an optical lens which is capable of being easily fitted in a cavity of a lens holder with high positioning accuracy.
As well known, an electronic data processing equipment such as a personal computer is connected to various peripheral devices which include a memory device. As the memory device, an optical disk memory device can be used.
The optical disc memory device is, for example, a CD-R drive which can write/read data to/From a CD-R (compact disc recordable) as a recording medium by using a laser beam. The CD-R is a write-once optical disc that allows additional writing many times but does not allow erasing data recorded thereon. The CD-R can be used for a CD-ROM or a CD-DA (audio CD) because the data recorded thereon can be read by a normal CD-ROM drive.
The optical disc memory device has an optical pickup to apply the laser beam on a surface of the recording medium and to detect the reflection from the surface. The optical pickup includes a laser beam source for emitting the laser beam, an object or optical lens for gathering the laser beam from the laser beam source on the surface of the recording medium, and a lens holder for holding the object lens.
The lens holder has a through-hole for passing the laser beam through therein. A part of the through-hole serves as a cavity for receiving the object lens. Generally, the cavity is larger than the other part of the through-hole in inner diameter.
In a conventional technique, the object lens is fitted in the cavity of the lens holder by a running (or free) fit method or an interference fit method.
In the running fit method, there is a problem that it is difficult to put the object lens in a desired position of the cavity. In other wards, the running fit method can not position the object lens to the lens holder with high positioning accuracy. This is because there is a gap between a peripheral or outer side surface of the object lens and an inner side surface of the cavity. When the object lens is not in the desired position, it is impossible to obtain desired optical characteristics for the optical pickup.
On the other hand, the interference fit method does not have such a problem as the running fit method. However, the interference fit method has another problem that it is necessary to press the object lens with large pressing force in the cavity. The large pressing force deforms the object lens and deteriorates optical characteristics for the optical pickup.